1. Field of the Invention
This invention relates to a laser system, and particularly to an injection controlled laser system.
2. Discussion of Prior Art
In laser systems utilising broadband laser transitions or having unstable resonators, competition between different modes results in the laser power being spread over a number of modes. Examples of such laser systems are the CO.sub.2 and excimer lasers. These laser systems also exhibit net optical gain or amplifying properties for a gain period of a comparatively short duration. In particular, excimer lasers exhibit a relatively weak optical gain compared with other lasers. Much of the optical gain period may be devoted to amplifying weak spontaneous emission, which provides correspondingly weak laser output power. It is accordingly advantageous to provide amplification of desirable laser modes.
One known control technique involves injecting a pulse of laser radiation into the laser cavity. This technique provides the laser cavity with a starting flux of an intensity similar to the strong laser modes. Such a flux reduces the time necessary to establish a powerful laser field and a considerable increase in laser output power is achieved. Pulse injection also provides inter alia control of the laser output frequency. Examples of the utilisation of such a mechanism can be found in Applied Physics letters 36(8) pp 617-622, (15 April 1980) and in Applied Physics 23 pp 245-251 (1980).
Injection control is suited to laser systems whose media exhibit net gain for only a short duration, such as the CO.sub.2 and excimer lasers. However, this short duration of net gain produces timing problems. The injected pulse must appear when the laser medium is exhibiting net gain, i.e. in a certain `time window`. Prior art laser systems incorporating two lasers require complex activation mechanisms for the pumping systems to synchronise laser action. In practice, the two lasers are difficult to synchronise. Furthermore, separate laser systems are required, each involving a respective laser cavity, pumping and activation devices.